Filament



It is usual to construct thesefilaments' of some .Patentecl Au 29,a1933 .FILAMENT Allen B; Du Mont, Bloomfield, N Ji, assignor to i I De Forest Radio Company, Jersey City, 1..

. a corporation of Delaware No Drawing. Application November 7 Serial No. 321,844

'This invention relates in general to a metal alloy particularly adapted for use in constructing filaments for electron 'emi'ssive devices.

One of the objects of this invention is thepro-v vision of an alloy from which filamentsfor use in electron discharge devices maybe constructed 7 having desirable characteristics for such use.

Another object of this invention is the provision of filaments of this 'type .which have a higher tensile strength than filaments-of this type now known.

Another object of this invention is the provision of filaments made from the improved alloy having a-high electron emissivity. A further object of this invention is the prochromium iron alloy. v

"These and other objects will appear from the following disclosure are sought by means of this inventionr This invention resides substantially in the combination, construction, and proportion of parts duction' of a gfilament composed'of a nickel as will bemore fully disclosed hereinafter.

Electron discharge devices, of which the audion used in radio receiving and transmitting apparatus is an example, employ an electronically active element generally known as a cathode. These cathodes are usually provided with a coating of highly emissive sub'st'ance which when heated throws oif electrons in large quantities.

metal such as nickel or platinum which is coated with the elctron emissivesubstance. Filaments of .nickel or platinum, however, have many dis- T advantages, such as extremely small cross sectionalarea when constructed for the correct cur;

.rentcarryingcapacities for use on voltages now common in operating radio receiving and transmitting apparatus, and as a result are very 40 fragile. r i 1 a The filament of this invention is made of a metal alloy and is of relatively large cross sectional area when madefor'use in apparatus of this'type and is, therefore, much more rugged, having a higher tensile strength, and acts better as a cathode by reason of the larger area-from which the electrons can be emitted. Furtherupon to dissipate as much heat as they would when employing altungsten filament"which is easily heated to a whitehot-incandescence.. The, 1 absence of this excess heat produces better opera L;

ating characteristics.- j '1 9 The filament is constructed of a metal alloy comprising nickel, chromium andxironr In the. bestpracticethe proportions arejchromium 15%, iron 20%, and nickel r A metal alloy of nickel, iron and chromium inthese percentages 5 produces a filament having the characteristics at 750 degrees centigr'ade as contrasted with 2300 degrees centigrade for the usual thoriated ,tung sten filament. At 3 volts this filament gives about 0 the same emission'as theIusual thoriatedtungsten filament at full '5 volts, while the life of this. filament is several times as great as that of a corresponding thoriated tungsten filament.

It is, of course, to be understood that'good results'can be secured inaccordancewith this inf vention'by varying the proportions given and I do not, therefore. desire -to' be structurally limited to the exact-proportions given but to a range of equivalent proportions which produce a filament of substantially the same characteristics.

' What I seek to'secureby United States Let- 'ters'Patent is: j g A filament for electron discharge devices com prising a metal alloy consisting of approximately H 15% chromium, iron 20%,. and approximately 65% nickel, whereby'the filament may be effec-v tively operated as an emitter at a dull redheat;

. and a coating of electron emissivematerial on 0 more, coated filaments of this nature are found to have anelectroniemissivity which is three times greater than theemissivity of thoriated tungsten filament, In addition, by reason of its relatively greater size the filament is operated at a much lowerte'mperatureand, in fact, at a very dull red heat so as to be hardly visible. The

result is thatdevices of this nature are not called 

